Field of the Invention
The invention relates to a method for dewatering and separating animal process wastewater, vegetable and fruit waste and other industrial and municipal waste and post-waste streams using a liquefied gas solvent in a rotary pressure filter to yield one or more proteins, lipids and/or other useful biomass extracts.
Description of the Related Technology
Various types of separation and extraction processes are employed to recover materials dissolved or suspended in waste streams. Many separation methods, solvents, gases and apparatus exist to separate different types and volumes of biomass into useful by-products with a wide range of values, from commodities to value added ingredients. In the animal processing waste product industry, dissolved air flotation and other flocculation processes with or without some combination with centrifuge processes are used most often to separate saleable by-products, such as lipids, from the animal processing wastewater streams. However, much of the value in lipids and proteins remain in the post-flocculated material commonly known as “DAF” (“DAF” is an acronym for “dissolved air flotation” and sometimes also is used in reference to the resulting material after dissolved air flotation processing). While poultry, beef, pork, dairy and fish waste streams respond differently to flocculation and centrifuge processes, significant quantities of valuable by-products still remain in the waste stream. By contrast, fruit, vegetable and other botanical matter may employ different processes for recovering saleable by-products which apply extensive heat and pressure to produce certain extracts, although the heat and pressure can damage the resultant products in ways that limit usefulness and therefore their value.
Others have described methods and systems to process “DAF” and other waste materials. For example, U.S. Pat. No. 7,186,796 provides a method of isolating a bio-molecule including peptides, proteins, polynucleotides and polysaccharides from a water-borne mixture by contacting the water-borne mixture with dimethyl ether to precipitate solid particles of the bio-molecule. The water-borne mixtures include aqueous solutions, suspensions, emulsions, micro-emulsions and liposomes suspended in aqueous media. Similarly, U.S. Pat. No. 7,897,050 provides a method and system for the extraction of an organic chemical constituent, including hydrocarbons, crude petroleum products, refined petroleum products, synthetic compounds from a solid matter, including from animal renderings, using an inclined auger in a pressurized chamber. Thus, prior art systems have focused on higher value input streams, and generally worked with smaller volumes of waste materials where the methods, apparatus and chemistry can yield a higher value output. Prior art has been limited by the cost to scale the process in the form of cost prohibitive capital equipment needed to process large volumes of waste streams and/or the operating cost in the form of energy required to separate the waste streams into valuable commodity products.
In principle, continuously and discontinuously operating pressing apparatuses, e.g. multi-platen presses, strainer presses, plate filter presses, travelling screen presses and screw presses, are suitable for separating off the lipids and proteins from the biomass. Centrifuges are likewise suitable for separating off lipids from the biomass. Known types of centrifuges include, for example, turnout centrifuges, peeler centrifuges, pusher centrifuges, mesh screw centrifuges, vibrating centrifuges and sliding centrifuges and decanters. See, e.g., WO 2010/001492 A1, relating generally to recovering tallow and more particularly, to removing fats, oil and grease and recovering tallow from food or animal processing wastewater by adding a flocculant and separating the tallow from the solids employing a centrifuge.
A further method which has attained importance for separating lipids and proteins from a biomass is filtration. A distinction is made between discontinuous and continuous filtering systems. Discontinuously operating filters include, for example, fixed-bed filters, suction filters, candle filters, leaf filters and plate filters. The separation of lipids and protein from the biomass by means of discontinuously operating filters is generally less preferred. A disadvantage here is the loading and unloading of the filter, which requires a considerable time, as well as filter clogging related to lipid viscosity exacerbated by lower processing temperatures where liquefied gases are employed. It is a further disadvantage that DAF, in aqueous solution, yields flux rates that make traditional commercial filters unusable. Thus, discontinuously operating filters are not suitable for large biomass throughputs. Large biomass throughputs can be categorized as several tons of input waste per hour.
Continuously operating filters, such as belt filters and rotary filters, also have been found to be useful as separation apparatuses, and rotary pressure filters as are known from WO 02/100512 A1 are particularly suitable.
Generally, solvent extraction can be used to increase the yield of recovered lipids and protein from biomass waste streams. However, solvent extraction produces a solvent-extracted residue which contains residual solvent. Consequently, there is a need for a method for separating lipids and proteins from biomass waste streams providing a useful product having an acceptably low residual solvent content and correspondingly low toxicity effects.
There remains a need to create energy- and economically-efficient systems to extract solutes such as lipids and proteins from post waste biomass materials, such as animal “DAF”, flocculated and nonflocculated animal, vegetable and fruit wastestreams and other matter. The present invention addresses these and other needs.